The first prototype of the B-52 may have been designed in a weekend. The B-52 of today was iteratively designed over decades and the current H models are entirely different planes than earlier models (although structurally very close to the G model). Another HN commenter mentioned GPS being designed over a holiday. But we spent years and years in the military debugging GPS and making it functional. Claiming that some…
It's honestly a fantastic case for incremental improvements over time. There's practically no single part on a modern B-52 that's original to the 1960s since everything has been overhauled and modernized decade by decade. Every attempt to replace it has been (or will be) retired before its EOL.
The trick is to design something solid enough to be a good base for incremental improvements over time.